In recent years, a circuit body (so-called wire harness) for connecting a power supply or the like mounted on a vehicle to various electrical components or the like is known. Generally, this type of the circuit body is constituted so as to be able to realize appropriate supply of electric power from a main power supply such as an alternator (power generator) and a battery to a large number of electrical components (for example, ECU and various auxiliary devices), appropriate switching of power supply or cutoff, transmission of various communication signals, and the like.
Specifically, this type of the circuit body (wire harness) is generally constituted of a wire bundle which is an aggregate of various kinds of electric wires connecting a power supply and electrical components, a junction block for distributing electric power to a plurality of systems, a relay box for controlling supply or cutoff of electric power to each system, fuse box which protects wires and electrical components from excessive current, and the like (see JP-A-2005-78962, for example).